#VU71486 Race condition in Samba - CVE-2021-20251

Vulnerability identifier: #VU71486

Vulnerability risk: Low

CVSSv4.0: 0.6 [CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: CVE-2021-20251

CWE-ID: CWE-362

Exploitation vector: Local network

Exploit availability: No

Vulnerable software:
Samba
Server applications / Directory software, identity management

Vendor: Samba

Description

The vulnerability allows a remote attacker to perform a brute-force attack.

The vulnerability exists due to a race condition in Samba when incrementing bad password attempts. Each connection to Samba gets a separate process, and each process loads, increments, and saves the bad password count without any coordination. A remote attacker can perform a brute-force attack using multiple threats and bypass imposed limits on the number of allowed incorrect passwords.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Samba: 4.1.0 - 4.17.0, 4.2.0 - 4.2.14, 4.3.0 - 4.3.13, 4.4.0 rc4 - 4.4.16, 4.5.0 - 4.5.16, 4.6.0 - 4.6.16, 4.7.0 - 4.7.12, 4.8.0 - 4.8.12, 4.9.0 - 4.9.18

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External links
https://bugzilla.samba.org/show_bug.cgi?id=14611
https://gitlab.com/samba-team/samba/-/merge_requests/2708

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the local network (LAN).

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.